Process of making decolorized tannin extracts.



UNITED STATES PATENT OFFICE.

GEORG KLENK, OF HAMBURG, GERMANY.

PROCESS OF MAKING DECOLORIZED TANNIN' EXTRACTS.

SPECIFICATION forming part of Letters Patent No. 720,157, dated February 10, 1903.

Application filed June 16,1902. Serial No. 111,990- (No specimens.)

To all whom, it may concern:

Be it known that I, GEORG KLENK, doctor of philosophy, a subject of the German Emperor, residing at Hamburg, Germany, (and whose post-office address is Billhornerkanalstrasse, Hamburg, Germany,) have invented certain new and useful Improvements in the Manufacture of Tannin Extracts, (for which I have applied for a patent in Germany on November 25, 1901,) of which the following is a specification.

The present invention chiefly consists in treating the crude tannin extracts or tannin solutions at boiling temperature with alumina sulfate, and subsequently with sodium bisulfite. During this treatment the alumina sulfate has at first an intense decolorizing effect, after which it interacts with the bisulfite in the manner represented by the following equation:

The alumina hydrate in a nascent state produced in this manner attracts the separated particles held in suspension andv falls to the bottom, thereby clarifying and decolorizing the liquid. The sulfurous acid also obtained in a nascent state has a decolorizing efiect and escapes almost completely during the concentration or boiling down of the liquor. The complete separation of the alumina out of the liquid is absolutely necessary, because otherwise extracts would be obtained which are decolorized, but which lack the easy and clear solubility in cold water, which are necessary. For completely separating the alumina a slight excess of bisulfite is required, which renders the extract limpid and easily soluble. Extracts produced in this manner are soluble in cold water. They possess and retain a decidedly-acid reaction and impart to the leather a fine light yellow color, differing but slightly or not all from that which is produced by oak tanning.

The addition of organic acids, such as lactic and acetic acid, and even of mineral acids, such as sulfuric acid, to the liquid extracts or solution of extracts will not produce any precipitate. Consequently there is no danger that in commercial working precipitates will be produced by the acid tanning liquors.

Moreover, the color which these extracts impart to the leather is permanentnot liable to change under the ordinary in fluence of the atmosphere.

In the commercial application of the process I proceed as follows: To the hot tannin extracts coming from the extractors I add a solution of alumina sulfate in a vat provided with an agitator, the quantity of the alumina sulfate to be employed depending on the strength of the tannin liquor, and the two liquids are thoroughly mixed by means of the agitator, whereby the liquor is decolorized, after which the required quantity of sodium bisulfite is added while constantly stirring. Subsequently the liquid is drawn off into a clearingvat,where the alumin a hydrate,which has been separated out, settles at the bottom, together with any solid impurities suspended in the liquid mixture. It is advantageous to cool the liquor to a temperature of 20 to 25 centigrade before drawing it off into the clearing-vat, whereby the extract gains in solubility and clearness.

A tannin liquor of 4 Baum requires for five thousand liters of the liquor about four kilograms of solid alumina sulfate and fifteen to twenty kilograms of sodium bisulfite of 38 to 40 Baum.

Quebracho extracts made from tannin liquors clarified and decolorized in the manner described above contain when at 25 Baum from forty-five to forty-six per cent. of tanmm.

It is evident that instead of alumina sulfate alum may be employed and instead of sodium bisulfite sodium sulfite and sodium hydrate, provided that the necessary precautions are observed.

The above process is suitable for the production of the following extracts soluble in cold water, viz: extracts of quebracho, mimosa, hemlock, sumac, firs, oak, chestnuts, and others.

What I claim is- 1. The process for the manufacture of decolorized tannin extracts soluble in cold water, which consists in first treating the crude tannin solution with alumina sulfate and subsequently with sodium bisulfite, substantially as described.

2. The process for the manufacture of tan min extracts soluble in cold water, which consists in adding to the hot crude tannin extracts a solution of alumina sulfate, thoroughly mixing the two liquids and subsequently adding sodium bisulfite, while constantly stirring,

and drawing off the liquid, substantially'as described.

3. The process for the manufacture of tannin extract soluble in cold water, which consists in adding to the hot crude tannin extract a solution of alumina sulfate, thoroughly mixing the two liquids, subsequently adding sodium bisulfite, while constantly stirring, then allowing the liquid mixture to cool to a temperature between 20 and 25 centigrade, then drawing olf and allowing it to settle, substantially as described.

4. The process for the manufacture of tannin extract soluble in cold water from a crude tannin solution of 4 Baum,which conwitnesses.

GEORG KLENK. Witnesses:

HERMAN REIMER, CLAUS RAMPMANN. 

